In the operation of variable displacement pumps which have a movable swash plate, a biasing means is generally used to place a predetermined biasing force on a spool of a servo valve for controlling the movement of the swash plate by the servo valve. It has been discovered, however, that the pump can be more effectively operated if the preselected biasing means of the servo valve can be varied under different load conditions and requirements. U.S. Pat. No. 3,864,063 which issued on Feb. 4, 1975 to R. J. Martin from an application filed Sept. 11, 1973 and which is assigned to The Cessna Aircraft Co., shows a servo valve having a plurality of biasing means to provide biasing force changes.
However, since the load characteristics and requirements of a hydraulic system are so extremely variable between different hydraulic systems, it is desirable to provide means for fine tuning a servo valve to more exactly match a preselected plurality of biasing forces of a servo valve to the load characteristics and requirements of a particular system upon which the variable displacement pump and its associated controls are to be used.
This invention therefore resides in a pump control assembly for a variable displacement pump which has an adjustable biasing means for providing improved control of the pump.